1. What happens to runt frames received by a Cisco Ethernet switch?

In an attempt to conserve bandwidth and not forward useless frames, Ethernet devices drop frames that are considered to be runt (less than 64 bytes) or jumbo (greater than 1500 bytes) frames.

2. What are the two sizes (minimum and maximum) of an Ethernet frame? (Choose two.)

56 bytes

64 bytes*

128 bytes

1024 bytes

1518 bytes*

Explanation:

The minimum Ethernet frame is 64 bytes. The maximum Ethernet frame is 1518 bytes. A network technician must know the minimum and maximum frame size in order to recognize runt and jumbo frames.

3. What statement describes Ethernet?

It defines the most common LAN type in the world.*

It is the required Layer 1 and 2 standard for Internet communication.

It defines a standard model used to describe how networking works.

It connects multiple sites such as routers located in different countries.

Explanation:

Ethernet is the most common LAN protocol in the world. It operates at Layer 1 and 2, but is not required for Internet communication. The OSI model is used to describe how networks operate. A WAN connects multiple sites located in different countries.

4. Which two statements describe features or functions of the logical link control sublayer in Ethernet standards? (Choose two.)

Logical link control is implemented in software.*

Logical link control is specified in the IEEE 802.3 standard.

The LLC sublayer adds a header and a trailer to the data.

The data link layer uses LLC to communicate with the upper layers of the protocol suite.*

The LLC sublayer is responsible for the placement and retrieval of frames on and off the media.

Explanation:

Logical link control is implemented in software and enables the data link layer to communicate with the upper layers of the protocol suite. Logical link control is specified in the IEEE 802.2 standard. IEEE 802.3 is a suite of standards that define the different Ethernet types. The MAC (Media Access Control) sublayer is responsible for the placement and retrieval of frames on and off the media. The MAC sublayer is also responsible for adding a header and a trailer to the network layer protocol data unit (PDU).

5. What statement describes a characteristic of MAC addresses?

They must be globally unique.*

They are only routable within the private network.

They are added as part of a Layer 3 PDU.

They have a 32-bit binary value.

Explanation:

Any vendor selling Ethernet devices must register with the IEEE to ensure the vendor is assigned a unique 24-bit code, which becomes the first 24 bits of the MAC address. The last 24 bits of the MAC address are generated per hardware device. This helps to ensure globally unique addresses for each Ethernet device.

6. Which statement is true about MAC addresses?

MAC addresses are implemented by software.

A NIC only needs a MAC address if connected to a WAN.

The first three bytes are used by the vendor assigned OUI.*

The ISO is responsible for MAC addresses regulations.

Explanation:

A MAC address is composed of 6 bytes. The first 3 bytes are used for vendor identification and the last 3 bytes must be assigned a unique value within the same OUI. MAC addresses are implemented in hardware. A NIC needs a MAC address to communicate over the LAN. The IEEE regulates the MAC addresses.

7. Which destination address is used in an ARP request frame?

0.0.0.0

255.255.255.255

FFFF.FFFF.FFFF*

127.0.0.1

01-00-5E-00-AA-23

Explanation:

The purpose of an ARP request is to find the MAC address of the destination host on an Ethernet LAN. The ARP process sends a Layer 2 broadcast to all devices on the Ethernet LAN. The frame contains the IP address of the destination and the broadcast MAC address, FFFF.FFFF.FFFF.

8. What addressing information is recorded by a switch to build its MAC address table?

the destination Layer 3 address of incoming packets

the destination Layer 2 address of outgoing frames

the source Layer 3 address of outgoing packets

the source Layer 2 address of incoming frames*

Explanation:

A switch builds a MAC address table by inspecting incoming Layer 2 frames and recording the source MAC address found in the frame header. The discovered and recorded MAC address is then associated with the port used to receive the frame.

9. Refer to the exhibit. The exhibit shows a small switched network and the contents of the MAC address table of the switch. PC1 has sent a frame addressed to PC3. What will the switch do with the frame?

The switch will discard the frame.

The switch will forward the frame only to port 2.

The switch will forward the frame to all ports except port 4.*

The switch will forward the frame to all ports.

The switch will forward the frame only to ports 1 and 3.

Explanation:

The MAC address of PC3 is not present in the MAC table of the switch. Because the switch does not know where to send the frame that is addressed to PC3, it will forward the frame to all the switch ports, except for port 4, which is the incoming port.

10. Which switching method uses the CRC value in a frame?

cut-through

fast-forward

fragment-free

store-and-forward*

Explanation:

When the store-and-forward switching method is used, the switch receives the complete frame before forwarding it on to the destination. The cyclic redundancy check (CRC) part of the trailer is used to determine if the frame has been modified during transit.​​ In contrast, a cut-through switch forwards the frame once the destination Layer 2 address is read. Two types of cut-through switching methods are fast-forward and fragment-free.

11. What is auto-MDIX?

a type of Cisco switch

an Ethernet connector type

a type of port on a Cisco switch

a feature that detects Ethernet cable type*

Explanation:

Auto-MDIX is a feature that is enabled on the latest Cisco switches and that allows the switch to detect and use whatever type of cable is attached to a specific port.​​

12. True or False?

When a device is sending data to another device on a remote network, the Ethernet frame is sent to the MAC address of the default gateway.

true*

false

Explanation:

A MAC address is only useful on the local Ethernet network. When data is destined for a remote network of any type, the data is sent to the default gateway device, the Layer 3 device that routes for the local network.

13. The ARP table in a switch maps which two types of address together?

Layer 3 address to a Layer 2 address*

Layer 3 address to a Layer 4 address

Layer 4 address to a Layer 2 address

Layer 2 address to a Layer 4 address

Explanation:

The switch ARP table keeps a mapping of Layer 2 MAC addresses to Layer 3 IP addresses. These mappings can be learned by the switch dynamically through ARP or statically through manual configuration.

14. Refer to the exhibit. PC1 issues an ARP request because it needs to send a packet to PC2. In this scenario, what will happen next?

PC2 will send an ARP reply with its MAC address.*

RT1 will send an ARP reply with its Fa0/0 MAC address.

RT1 will send an ARP reply with the PC2 MAC address.

SW1 will send an ARP reply with the PC2 MAC address.

SW1 will send an ARP reply with its Fa0/1 MAC address.

Explanation:

When a network device wants to communicate with another device on the same network, it sends a broadcast ARP request. In this case, the request will contain the IP address of PC2. The destination device (PC2) sends an ARP reply with its MAC address.

15. Refer to the exhibit. A switch with a default configuration connects four hosts. The ARP table for host A is shown. What happens when host A wants to send an IP packet to host D?

Host A sends an ARP request to the MAC address of host D.

Host D sends an ARP request to host A.

Host A sends out the packet to the switch. The switch sends the packet only to the host D, which in turn responds.

Host A sends out a broadcast of FF:FF:FF:FF:FF:FF. Every other host connected to the switch receives the broadcast and host D responds with its MAC address.*

Explanation:

Whenever the destination MAC address is not contained within the ARP table of the originating host, the host (host A in this example) will send a Layer 2 broadcast that has a destination MAC address of FF:FF:FF:FF:FF:FF. All devices on the same network receive this broadcast. Host D will respond to this broadcast.

16. Refer to the exhibit. The switches are in their default configuration. Host A needs to communicate with host D, but host A does not have the MAC address for its default gateway. Which network hosts will receive the ARP request sent by host A?

only host D

only router R1

only hosts A, B, and C

only hosts A, B, C, and D

only hosts B and C

only hosts B, C, and router R1*

Explanation:

Since host A does not have the MAC address of the default gateway in its ARP table, host A sends an ARP broadcast. The ARP broadcast would be sent to every device on the local network. Hosts B, C, and router R1 would receive the broadcast. Router R1 would not forward the message.

17. Which statement describes the treatment of ARP requests on the local link?

They must be forwarded by all routers on the local network.

They are received and processed by every device on the local network.*

They are dropped by all switches on the local network.

They are received and processed only by the target device.

Explanation:

One of the negative issues with ARP requests is that they are sent as a broadcast. This means all devices on the local link must receive and process the request.

18. What are two potential network problems that can result from ARP operation? (Choose two.)

Network attackers could manipulate MAC address and IP address mappings in ARP messages with the intent of intercepting network traffic.*

Large numbers of ARP request broadcasts could cause the host MAC address table to overflow and prevent the host from communicating on the network.

Multiple ARP replies result in the switch MAC address table containing entries that match the MAC addresses of hosts that are connected to the relevant switch port.

Explanation:

Large numbers of ARP broadcast messages could cause momentary data communications delays. Network attackers could manipulate MAC address and IP address mappings in ARP messages with the intent to intercept network traffic. ARP requests and replies cause entries to be made into the ARP table, not the MAC address table. ARP table overflows are very unlikely. Manually configuring static ARP associations is a way to prevent, not facilitate, ARP poisoning and MAC address spoofing. Multiple ARP replies resulting in the switch MAC address table containing entries that match the MAC addresses of connected nodes and are associated with the relevant switch port are required for normal switch frame forwarding operations. It is not an ARP caused network problem.

19. Fill in the blank.

A collision fragment, also known as a RUNT frame, is a frame of fewer than 64 bytes in length.

Explain:
A runt frame is a frame of fewer than 64 bytes, usually generated by a collision or a network interface failure.

20. Fill in the blank.

On a Cisco switch, port-based memory buffering is used to buffer frames in queues linked to specific incoming and outgoing ports.

21. Fill in the blank.

ARP spoofing is a technique that is used to send fake ARP messages to other hosts in the LAN. The aim is to associate IP addresses to the wrong MAC addresses.

Explain:
ARP spoofing or ARP poisoning is a technique used by an attacker to reply to an ARP request for an IPv4 address belonging to another device, such as the default gateway.

22. Match the characteristic to the forwarding method. (Not all options are used.)

A store-and-forward switch always stores the entire frame before forwarding, and checks its CRC and frame length. A cut-through switch can forward frames before receiving the destination address field, thus presenting less latency than a store-and-forward switch. Because the frame can begin to be forwarded before it is completely received, the switch may transmit a corrupt or runt frame. All forwarding methods require a Layer 2 switch to forward broadcast frames.

New Questions 2019.

23. What is the minimum Ethernet frame size that will not be discarded by the receiver as a runt frame?

64 bytes*
512 bytes
1024 bytes
1500 bytes

Explanation:

The minimum Ethernet frame size is 64 bytes. Frames smaller than 64 bytes are considered collision fragments or runt frames and are discarded.

24. What is a characteristic of port-based memory buffering?

All frames are stored in a common memory buffer.Frames are buffered in queues linked to specific ports.*
All ports on a switch share a single memory buffer.
Frames in the memory buffer are dynamically linked to destination ports.

Explanation:

Buffering is a technique used by Ethernet switches to store frames until they can be transmitted. With port-based buffering, frames are stored in queues that are linked to specific incoming and outgoing ports.